Authorities are searching for a healthcare reform activist today who they said bit off the finger of a 65-year-old counter-demonstrator during a fight at a MoveOn.org rally in Thousand Oaks.

“It all started with their difference in philosophy over healthcare reform,” said Senior Deputy Eric Buschow of the Ventura County Sheriff’s Department.

The incident occurred about 7 p.m. Wednesday at a “We Can’t Afford to Wait Vigil” organized by affiliates of the activist group MoveOn.org, which drew supporters of President Obama’s healthcare plan, Buschow said. The rally also attracted several counter-protesters, he said.

During the rally at Lynn Road and Hillcrest Drive, near the Oaks Mall, the two men got into a heated argument and began fighting.

“At which point, one man bit off the left pinky of the other,” Buschow said.

The injured demonstrator then drove himself to Los Robles Hospital and Medical Center about a mile away, he said.

Ilyse Hogue, director of political advocacy and communications for MoveOn.org, called the incident “a regrettable act of violence” in a statement released this morning.

“While we do not have any more facts about what happened than what we saw in press accounts, MoveOn condemns violence in all forms,” Hogue said. “We support the Ventura County sheriff’s investigation into the situation. It is in our firm hope that this event does not detract from the tens of thousands who were out peacefully making their voices heard for health care reform and a public option.”

Authorities said they are looking for a white male in his late 40s or 50s who was last seen wearing black shorts and a black shirt.

“We’re still trying to figure out who was the aggressor,” Buschow said.